Observation on opae ula and areas of lower-salinity water.

[Fishkeeper]

I've had some bad fatigue issues lately (for known, non-dangerous reasons), and as a result haven't been topping off my opae tank, since they really don't care if their salinity very slowly rises for awhile. I've now started the process of slowly raising it back up, by using a piece of airline tubing, tied in a knot so it drips slowly, to add RODI water in.

The end of the tube is touching the bottom of the tank, so the water will mix in some, but it's still produced a layer of less saline water on top of the tank. I can tell it's there because the shrimp are largely staying below that level, and I see the tell-tale ripples of salinities mixing whenever one gets close. They're showing a behavior I only see during larger top-offs, where practically the entire population is busy running/swimming along the walls, going in circles (squares) around the tank. They clearly aren't distressed, their colors are excellent, so maybe they think it's rained and may have washed food in?

The reason I'm commenting here is because, though they're mostly staying below that area of less saline water, they are going up into it now and then. Clearly a deliberate motion up, and then dipping back down after a second or two. Which surprised me, because I would have thought going into a different salinity so quickly wouldn't feel good. Maybe the brief lower salinity doesn't have a chance to impact them? Maybe it's mildly uncomfortable, but not enough to deter them from curiosity and investigation? I'm not sure what, if anything, they want in that layer.

I also saw a little floating larva steadily rise up through the whole tank, until it hit the barrier between salinities, at which point it stopped like one of those little floats in an experiment to demonstrate different liquid densities. I suppose whatever it was doing to rise doesn't work so well in lower density water, as it stopped perfectly right at the edge. This isn't particularly relevant, since it didn't go into the less dense water- I just thought it was funny. I wonder if it was confused, as much as a shrimp larva can be, about why it stopped.

[Tiny Ocean]

That's interesting. I wonder what that behavior means.

I am sorry you have been ill. Chronic fatigue (descriptively, whether that is the diagnosis or not) is more debilitating than most people understand.